Any integrated circuit (IC) device typically includes a number of input/output (I-O) circuitry to communicate information with the outside world. Different types of I-Os may be used in a chip that supports different signal voltage levels, current drives, data protocol, and data rates. I-Os, like all other circuits on the chip, are subject to random defects and statistical process variations, which may render them faulty. Consequently, the I-O circuits are tested to ensure they meet their advertised specifications. The I-O test methodology employed strongly depends on the type of the I-O in general. However, almost all types of I-O are tested for DC parameters because such tests reveal a significant portion of faults very quickly.
The most widely used DC test methodologies are based on automatic test equipment (ATE). Each I-O is connected to an external tester pin, through which the I-O connects to a parametric measurement unit (PMU). The PMU is capable of forcing voltage and measuring current or forcing current and measuring voltage. These capabilities enable the PMU to perform a wide variety of tests, such as output voltage, drive current, leakage current, and input voltage threshold tests. Such testers may use serial or parallel approach to test all the I-Os connected to the ATE pins. Although flexible and fast, the use of ATE for I-O test is becoming increasingly expensive because of large tester pin requirements.